Method for processing perfluorocarbon, and apparatus therefor

ABSTRACT

An exhaust gas containing a perfluoride compound (PFC) and SiF 4  is conducted into a silicon remover and brought into contact with water. A reaction water supplied from a water supplying piping and air supplied from an air supplying piping are mixed with the exhaust gas exhausted from the silicon remover. The exhaust gas containing water, air, and CF 4  is heated at 700° C. by a heater. The exhaust gas containing PFC is conducted to a catalyst layer filled with an alumina group catalyst. The PFC is decomposed to HF and CO 2  by the catalyst. The exhaust gas containing HF and CO 2  at a high temperature exhausted from the catalyst layer is cooled in a cooling apparatus. Subsequently, the exhaust gas is conducted to an acidic gas removing apparatus to remove HF. In this way, the silicon component is removed from the exhaust gas before introducing the exhaust gas into the catalyst layer. Therefore, the surface of the catalyst can be utilized effectively, and the decomposition reaction of the perfluoride compound can be improved.

This application is a Continuation-in-part application of Ser. No.09/190,853, filed Nov. 12, 1998 now abandoned, the contents of which areincorporated herein by reference in their entirety.

BACKGROUND OF THE INVENTION

The present invention relates to a method of processing perfluorocarbonand an apparatus therefor, and more particularly, the invention relatesto a preferable method for use in processing perfluorocarbon(hereinafter, called PFC) contained in an exhaust gas from asemiconductor manufacturing plant, and an apparatus therefor.

In a known semiconductor manufacturing process, various uses are made ofPFC gases, which are harmless to a human being, are nonexplosive, andare easy to handle, such as CF₄ and the like, which are used as anetchant in a dry etching process, and C₂F₆ and the like, which are usedas a cleaning gas in a CVD process. These PFC gases are ionized by aplasma discharge of a high voltage after being introduced into anetching apparatus or a CVD apparatus, and are used to perform etching orcleaning of wafers in an active radical state.

However, the amount of PFC gas actually consumed in the etching or thecleaning is several % to tens % by volume.

The rest of the PFC gas is exhausted outside the system in an unreactedstate.

TABLE 1 Properties of gas Consume Warm. Life.²⁾ Toxic. in Japan No PFCgas coeff.¹⁾ (year) react.³⁾ (t/year) Main use 1 CF₄ ⁴⁾ 6,300 50,000low- 300('94) Etching gas: 75% toxic. 394('95) CVD cleaning non- gas:25% flam.⁵⁾ 2 CF₆ ⁶⁾ 12,500 10,000 low-  4('94) P-CVD cleaning toxic,200('95) gas non- flam.⁵⁾ 3 NF₃ ⁷⁾ 9,720 179 toxic  25('94) CVD cleaning 39('95) gas: 92% IC-Etching gas: 8% 4 CHF₃ ⁸⁾ 12,100 250 —  55('94) dryetching 5 C₄F₈ ⁹⁾ 8,700 3,200 — — etching 6 C₃F₈ ¹⁰⁾ 7,000 2,600 — —P-CVD cleaning gas 7 SF₆ ¹¹⁾ 24,900 3,200 —  26('94) dry etching: 90%CVD cleaning gas: 10% Remarks: ¹⁾Warming-up coefficient ²⁾Life time inatmosphere ³⁾Toxicity and reactivity ⁴⁾Flon 14 ⁵⁾Non-flammable ⁶⁾Flon116 ⁷⁾Nitrogen trifluoride ⁸⁾Flon 23 ⁹⁾Flon C 318 ¹⁰⁾Flon 218 ¹¹⁾Sulfurhexafluoride

Because a fluorine atom has a small atomic radius and a strong bondingforce, PFC, a compound of fluorine atoms, has stable characteristics.PFC includes flon, such as FC (fluorocarbon) and HFC(hydrofluorocarbon), which do not include chlorine, and perfluoridecompounds, such as nitrogen trifluoride (NF₃) and sulfur hexafluoride(SF₆). Main materials of PFC, and their characteristics and main use,are indicated in Table 1.

PFC exists stably in the atmosphere for a long time, and, because itdoes not contain chlorine, its molecular structure is compact, and itsbonding force is strong. For instance, the life of CF₄ is as long as50,000 years, the life of C₂F₆ is 10,000 years, and the life of SF₆ is3,200 years. However, PFC has a large warming-up coefficient. Incomparison with CO₂, CF₄ is 6,500 times, C₂F₆ is 9,200 times, and SF₆ is23,900 times. Therefore, although a smaller amount of PFC is releasedthan CO₂, which is required to be decreased since it is a cause ofwarming-up of the earth, it is anticipated that the release of PFC willcertainly be restricted in the near future. In this case, acountermeasure against release of the exhaust gas from semiconductormanufacturing plants, which is the source of a majority of the PFC beingreleased, will become an important consideration.

For instance, in an etching step performed in a semiconductormanufacturing plant, a PFC gas for etching is supplied into a chamber. Apart of the PFC gas is converted to highly corrosive fluorine atoms byapplying a plasma thereto. The fluorine atoms perform an etching ofsilicone wafers. The exhaust gas from the chamber is pumped outcontinuously by a vacuum pump. In order to prevent corrosion by theacidic gas, purging of the exhaust gas with nitrogen gas is performed.The exhaust gas contains nitrogen in the amount of 99% and PFC in aresidual amount of 1%, which has not been used for the etching. Theexhaust gas pumped out by the vacuum pump is conducted to an acidremoving apparatus, through the duct for removing the acidic gas, and isreleased into the atmosphere in a state in which it contains the PFC.

In the semiconductor manufacturing plants, a reagent method and acombustion method have been used practically as a method ofdecomposition of PFC. The former is a method wherein fluorine ischemically fixed at approximately 400-900° C. by using a specialreagent. In accordance with this method, exhaust gas processing is notnecessary, because no acidic gas is generated by the decomposition. Thelatter is a method wherein the PFC gas is conducted to a combustor andis decomposed thermally in a flame of at least 1,000° C. generated bycombustion of LPG and propane gas.

In accordance with the above reagent method, the reagent which isreacted chemically with the PFC cannot be re-used, and the expensivereagent, which is consumed in the reaction as a consumable article, isrequired to be supplied frequently. Therefore, the operation cost is 10to 20 times in comparison with that of the combustion method.Furthermore, because an amount of the reagent equivalent to the amountof the PFC to be processed is necessary, practical equipment forperforming the reagent method requires a large area, such asapproximately 3-5 m².

In accordance with the above combustion method, thermal decomposition isperformed at a high temperature, such as at least 1,000° C. for C₂F₆ andat least 1,100° C. for CF₄, and a large amount of thermal energy isrequired. Furthermore, the combustion method generates NOx and a largeamount of CO₂ by combustion at a high temperature. Because the PFC isexhausted in a state in which it is diluted with inactive N₂ gas, apotential for miss-fire is high, and a sufficient operation control isrequired.

An application of the combustion method to the semiconductormanufacturing process has been studied. The PFC is exhausted as a mixedgas diluted with N₂ gas having a concentration of several %.Accordingly, in the combustion of the mixed gas, a large amount of airfor combustion is required in addition to a fuel gas. Consequently,because the amount of gas to be processed is increased, the size of theapparatus is increased, and the area for the apparatus is required to beas large as approximately 0.7-5 m².

For instance, when C₂F₆ is contained in the amount of 1% in an exhaustgas exhausted at 100 liter/min. from a semiconductor manufacturingprocess, the necessary amount of LPG to make the thermal decompositiontemperature at least 1,000° C. is 10 liter/min., and the necessaryamount of air is approximately 400 liter/min. with an excessive ratio of1.5. The total amount of the exhaust gas after the combustion becomesapproximately 500 liter/min., because oxygen in the air is consumed andCO₂ is generated at a rate of 30 liter/min. The total amount of theexhaust gas is increased almost 5 times that of the exhaust gasexhausted from the semiconductor manufacturing process. The typicalsemiconductor manufacturing plant has a large restriction on space,because the plant must be provided with clean rooms. Accordingly, it isdifficult to provide the necessary area for installing a new exhaust gasprocessing apparatus in a previously built semiconductor manufacturingplant.

On the other hand, a catalytic method, wherein PFC is decomposed atapproximately 400° C., has been applied to CFC (chlorofluorocarbon) andHCFC (hydrochlorofluorocarbon), which have similar chemical compositionswith PFC and an ozone destruction effect. Because CFC and HFC containchlorine atoms having a large atomic radius in their compositions, themolecular structures composed by bonding fluorine atoms and hydrogenatoms having a small atomic radius are distorted. Therefore, CFC and HFCcan be decomposed at a relatively low temperature.

A method of decomposing CFC (or HFC) using a catalyst was disclosed inJP-A-9-880 (1997). In accordance with this method, a mixed gas of heatedair, which is made up of a carrier gas, steam and CFC, is conducted to acatalyst layer. The temperature of the catalyst layer is approximately430° C., because CFC has a low decomposition temperature. The exhaustgas containing decomposed gases exhausted out of the catalyst layer iscooled rapidly with cooling water, in order to prevent generation ofdioxine.

SUMMARY OF THE INVENTION

The object of the present invention is to provide a method of processingperfluorocarbon using a catalyst, which can improve the decompositionreaction, and an apparatus therefor. It relates to technology to made anexhaust gas harmless by decomposing the perfluoride compound containedin the exhaust gas using a catalyst.

A first feature of the invention is in the steps of removing siliconcomponents from an exhaust gas containing a perfluoride compound and thesilicon components, and, subsequently, supplying the exhaust gascontaining the perfluoride compound, to which any of water or steam isadded, to a catalyst layer which is filled with a catalyst, to decomposethe perfluoride compound with the catalyst. The exhaust gas can be, forexample, exhaust gas exhausted from semiconductor manufacturingapparatus.

In accordance with the first feature of the invention, a closing of thepores formed on the catalyst by solid particles generated by a reactionof the silicon components in the exhaust gas with the water or the steamadded to the exhaust gas can be prevented, because the siliconcomponents in the exhaust gas to be supplied to the catalyst has beenremoved previously. Furthermore, in accordance with the first feature ofthe invention, choking intervals formed among the catalysts by the solidparticles can be prevented. Accordingly, since the surface of thecatalysts can be utilized effectively, the decomposition reaction of theperfluoride compound can be improved by this first feature of theinvention. The decomposition efficiency of the perfluoride compound canbe improved as well.

A second feature of the invention is in the step of removing acidic gasfrom a cooled exhaust gas. In accordance with this step, the acidic gascontained in the exhaust gas is decreased significantly.

A third feature of the invention is in the steps of removing siliconcomponents from the exhaust gas by using a first silicon componentsremoving apparatus and a second silicon components removing apparatus.The exhaust gas which flows out from the first silicon componentsremoving apparatus is supplied to the second silicon components removingapparatus to bring the exhaust gas into contact with water in the secondsilicon components removing apparatus. In the first silicon componentsremoving apparatus, the exhaust gas containing silicon components isbrought into contact with waste water from the second silicon componentsremoving apparatus and cooling water contacted with the exhaust gascontaining a decomposed gas.

Because the waste water from the second silicon components removingapparatus and cooling water contacted by the exhaust gas containing thedecomposed gas are contacted by the exhaust gas containing siliconcomponents in the first silicon components removing apparatus, a part ofthe silicon components contained in the exhaust gas is removed with amixed water of the waste water and the cooling water. Therefore, theamount of fresh water to be supplied to the second silicon componentsremoving apparatus can be decreased, and the overall amount of wastewater to be processed is decreased. Furthermore, since the siliconcomponents contained in the exhaust gas are processed twice so as to beremoved by the first and second silicon components removing apparatus,respectively, the efficiency of removal of the silicon components isimproved.

A fourth feature of the invention resides in the use of an alumina groupcatalyst as the catalyst for decomposing the perfluoride compound.

Because an alumina group catalyst is used, the perfluoride compound canbe decomposed effectively and conveniently at a reaction temperature inthe range of 650-750° C.

Particularly, the present invention is achieved based on findingsdescribed below, which are newly found by the present inventors:

-   -   (1) Silicon components (for instance, SiF₄) contained in an        exhaust gas exhausted from semiconductor manufacturing apparatus        generates silicon oxide (for instance, SiO₂) by reacting with        water, when water (or steam) necessary for a decomposing        reaction of perfluoride compound with catalyst is added to the        exhaust gas; and    -   (2) The silicon oxide chokes pores in the catalyst and spaces        among the catalyst particles, and decreases the perfluoride        decomposing efficiency of the catalyst.        In view of these findings, and to solve problems in connection        therewith, the present inventors found that choking of the        catalyst caused by the silicon oxide (a product of the reaction        of silicon components with water or steam) can be prevented by        removing the silicon components (for instance, SiF₄) from the        exhaust gas prior to adding water or steam to the exhaust gas        (for example, prior to adding the water or steam for reaction        with the perfluoride), and the perfluoride decomposing        efficiency can be improved.

Moreover, according to aspects of the present invention, siliconcomponents are removed from the exhaust gas (for instance, using ascrubber) prior to the addition of water or steam to the exhaust gas,especially, prior to the addition of water or steam necessary for thedecomposing reaction of the perfluoride. If the silicon components areremoved from the exhaust gas using a scrubber after adding water (orsteam) which is necessary for the decomposing reaction of perfluoride,to the exhaust gas, the added water might be removed from the exhaustgas simultaneously with the removal of silicon components.

Thus, if water (or steam) necessary for the decomposing reaction ofperfluoride is added to the exhaust gas which contains siliconcomponents, the silicon components react with the water or steam togenerate silicon oxide, and the water (or steam) necessary for thedecomposing reaction of perfluoride is consumed by reaction with thesilicon components. Accordingly, the water (or steam) necessary for thedecomposing reaction of perfluoride becomes deficient.

According to aspects of the present invention, the silicon componentsare removed prior to the addition of water (or steam) necessary for thedecomposing reaction of fluoride. Therefore, consumption of the water(or steam) necessary for the decomposing reaction of perfluoride by thereaction of the silicon components with this water (or steam) can beprevented, and decrease in the decomposing efficiency of perfluoride bylack of necessary water can be suppressed.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic diagram of an exhaust gas control system for a dryetching apparatus in a semiconductor manufacturing plant, in which apreferable embodiment of the present invention, i.e. a perfluorideprocessing apparatus, is applied thereto;

FIG. 2 is a schematic diagram showing the composition of a clean room,wherein the dry etching apparatus and the perfluoride compoundprocessing apparatus indicated in FIG. 1 are arranged;

FIG. 3 is a schematic diagram of the perfluoride compound processingapparatus indicated in FIG. 1 and FIG. 2;

FIG. 4 is a vertical cross section of the silicon remover indicated inFIG. 3;

FIG. 5 is a vertical cross section of the PFC decomposition processingunit indicated in FIG. 3;

FIG. 6 is a graph indicating decomposition characteristics of variousPFC by the alumina group catalyst;

FIG. 7 is a partial vertical cross section indicating an exchangingoperation of a catalyst cartridge indicated in FIG. 5;

FIG. 8 is a schematic diagram of another embodiment of the perfluorideprocessing apparatus indicated in FIG. 1;

FIG. 9 is a vertical cross section of another embodiment of the PFCdecomposition processing unit;

FIG. 10 a schematic diagram of another embodiment of the clean room,wherein another embodiment of the perfluoride compound processingapparatus and dry etching apparatus are arranged;

FIG. 11 is a schematic diagram of the perfluoride compound processingapparatus indicated in FIG. 10;

FIG. 12 is a cross section in the vicinity of the baffle plate indicatedin FIG. 11;

FIG. 13 is a vertical cross section of another embodiment of theperfluoride compound processing apparatus indicated in FIG. 1; and

FIG. 14 is a schematic diagram of another embodiment of the perfluoridecompound processing apparatus indicated in FIG. 1.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

A perfluoride compound processing apparatus (PFC gas processingapparatus), i.e. a preferred embodiment of the present invention appliedto an exhaust gas control system of an etching apparatus in asemiconductor manufacturing plant, will be explained hereinafter withreference to FIG. 1, FIG. 2, and FIG. 3.

PFC does not contain chlorine, and so its molecular structure iscompact, its bonding force is strong, and its decomposition temperatureis as high as approximately 700° C. Therefore, the catalytic method(disclosed in JP-A-9-880 (1997)), which could be applied to CFC and HFC,could not be applied to PFC. However, currently, the present inventorshave succeeded in development of an alumina group catalyst having areaction temperature at approximately 700° C. which is applicable to thedecomposition of PFC. Regarding the above catalyst, patent applicationshave been filed in the Japanese Patent Office as Japanese PatentApplications No. Hei 9-4349 (filed Jan. 14, 1997) and No. Hei 9-163717(filed Jun. 20, 1997). In accordance with the present embodiments, theabove catalyst is used for processing the exhaust gas.

In accordance with the exhaust gas control system of a dry etchingapparatus, for instance, each PFC processing apparatus 1, 1A, 1B, isconnected to a respective one of three dry etching apparatus 42, 42A,42B, as indicated in FIG. 1. Each of the dry etching apparatus comprisestwo etching regions 43A, 43B, partitioned in the apparatus.

In each of the etching regions, an etching process is performed forwafers by supplying CF₄, i.e. a PFC gas, as an etching gas. The exhaustgas from the etching regions 43A, 43B, is conducted to a PFC processingapparatus 1 through piping 44A, 44B, 29, by driving vacuum pumps 30A,30B. The exhaust gas contains approximately 1% of CF₄, which has notbeen consumed in the etching process, and SiF₄ generated by the etchingprocess. The exhaust gas is exhausted to the duct 45 after beingprocessed in the PFC processing apparatus 1 through the piping 36. Theexhausted gases from other dry etching apparatus 42A and 42B are alsoconducted to the duct 45 in the same way.

The exhaust gas in the piping 29 and the exhaust gas in the piping 36 isconducted to a gas chromatography unit 48 by sampling piping of 46A and46B, respectively. An acid gas filter 47 is provided in the samplingpiping 46A. Concentrations of CF₄ in the exhausted gases supplied to andexhausted from the PFC processing apparatus 1 are determined by the gaschromatography unit 48. The determined values on the concentration ofCF₄ in the exhausted gases are input from the gas chromatography unit 48to a monitoring apparatus 49. When the concentration of CF₄ in theexhausted gas in the piping 36 is higher than a first preset value, themonitoring apparatus 49 generates an alarm sound with flashing of awarning device 51 of the corresponding PFC processing apparatus forproviding a warning of an abnormal state. When the concentration of CF₄in the exhausted gas in the piping 29 is higher than a second presetvalue, the monitoring apparatus 49 generates an alarm sound withflashing of a warning device 50 of the corresponding dry etchingapparatus 42 for providing a warning of an abnormal state. Furthermore,the monitoring apparatus 49 checks for a normality of the catalyticreaction in the reactor 9, which will be explained later, and a catalystchange timing from deterioration of the catalyst, based on adecomposition ratio obtained from the concentrations of CF₄ at theentrance and the outlet of the PFC processing apparatus 1.

Next, an approximate arrangement of the above-mentioned exhaust gascontrol system in the clean rooms of the semiconductor manufacturingplant will be explained hereinafter with reference to FIG. 2. A building59 of the semiconductor manufacturing plant is composed of clean rooms53, 54, arranged above and below a grating 52, respectively. Air in theclean room 54 is cleaned by filters 55A, 55B and is conducted to theclean room 53 through the piping 57A, 57B by driving blowers 56A, 56B.The air is cleaned again by a filter 58. The clean room 53 has a highercleanliness than the clean room 54. The dry etching apparatus 42 isinstalled in the clean room 53, i.e. a manufacturing apparatus area. ThePFC processing apparatus 1, 1A, and the like, and the vacuum pumps 30A,30B, are installed in the auxiliary apparatus area in the clean room 54.The piping, such as piping 44A, duct 45, and the like, are arranged atthe piping area above the auxiliary apparatus area in the clean room 54.

A composition of the PFC processing apparatus will be explainedhereinafter with reference to FIG. 3. The compositions of the PFCprocessing apparatus 1A, 1B, are the same as the composition of the PFCprocessing apparatus 1. The PFC processing apparatus comprises a siliconremover 2, a heating apparatus 3, a reactor containing a catalyst layer11, a cooling apparatus 22, an acidic gas removing apparatus 98, ablower 59, a waste water pump 60, and a temperature controller 62. Theexhaust gas exhausted from the blower 30A is conducted to the duct 45through the silicon remover 2, the heating apparatus 3, the reactor 9,the cooling apparatus 22, the acidic gas removing apparatus 98, and theblower 59. The heating apparatus 3, the reactor 9, and the coolingapparatus 22 are assembled in an integral body, as indicated in FIG. 5,to form a PFC decomposition processing unit 76.

The detailed composition of the silicon remover 2 is indicated in FIG.4. The silicon remover 2 comprises a spray 26 and a diffusion portion 97filled with packing materials inside a vessel. The exhaust gascontaining CF₄, SiF₄, and the like as impurities is conducted into thevessel of the silicon remover 2 via the piping 29. The exhaust gasoutlet of the piping 29 in the vessel is oriented downwards. The exhaustgas flows upwards in the vessel, and passes through the diffusionportion 97 to diffuse and to flow in the vessel. Cooling water suppliedfrom a water supplying pipe 38 is sprayed through the spray 26. Thediffusion portion 97 increases the contacting ratio of the sprayed waterand the exhaust gas, and improves the performance for removal of theimpurities as explained later.

A reaction expressed by the following equation (1) is generated bybringing the SiF₄ contained in the exhaust gas into contact with thesprayed water, whereby the SiF₄ contained in the exhaust gas isdecomposed to SiO₂ and HF.SiF₄+2H₂O=>SiO₂+4HF  (1)

The generated SiO₂ is in the form of fine particles of a solid body, andis removed from the exhaust gas by the sprayed water concurrently withits generation. HF has a large solubility in water, and is removed fromthe exhaust gas by dissolution into water. The waste water containingSiO₂ and HF is conducted to the bottom portion of the acid gas removingapparatus 26 and through the piping 35. The impurities accompanied withthe exhaust gas can be removed, not by spraying with water, but bycontacting them with water by a bubbling method.

Because the outlet of the exhaust gas piping 29 is oriented downwards,sprayed water from the spray 26 is prevented from splashing and backflowing into the piping 26. The vessel of the silicon remover 2 is madeof vinyl chloride, which is corrosion resistant against HF, in order toprotect the vessel from the corrosion by HF, which is generated by thereaction expressed by the equation (1).

A ball check valve 100 is provided at the exhaust gas outlet portion ofthe silicon remover 2. The ball check valve 100 is arranged between thering shaped protrusion 28A and the protrusion 28B. Therefore, thesilicon remover 2 made of vinyl chloride is protected from receivingthermal damage by a back flow of hot gas from downstream, i.e. theheating apparatus 3, when the operation of the PFC processing apparatus1 is stopped.

The exhaust gas flowing out from the silicon remover 2 is conducted tothe PFC decomposition processing unit 76 through the piping 31.

Detailed composition of the PFC decomposition processing unit 76 isindicated in FIG. 5. The PFC decomposition processing unit 76 comprisesa heating apparatus 3, a reactor 9, and a cooling apparatus 22. A casing6 and an internal tube 7 are shared between the heating apparatus 3 andthe reactor 9. The diameter of the internal tube 7 is smaller at theupper portion than at the lower portion thereof. A lid 87 to beconnected to the piping 31 is provided on the upper end of the casing 6.A flange 12 of the internal pipe 7 is fixed to the flange 13 of thecasing 6 by bolts. The heating apparatus 3 and the reactor 9 arecomposed to form an integral body structure. The upper end portion ofthe internal tube 7 is restricted in movement in a horizontal directionby a cylindrical portion 14 provided on the lid 87. A ring shaped plate8 is provided on the internal tube 7.

The heating apparatus 3, which comprises an electric heater 4 andthermal insulating material 5 covering the heater, is arranged above thering shaped plate 8. The heater 4 and the insulating material 5 arearranged between the casing 6 and the internal tube 7. A gap 16 isformed between the casing 6 and the ring shaped plate 8. The gap 16prevents the casing 6 from conducting the heat of the high temperatureexhausted gas (700° C.) from the internal tube 7 and the ring shapedplate 8 and releasing the heat outside the casing 6. That means that aheat loss of the exhaust gas can be reduced. The structure of the PFCprocessing apparatus 1 can be simplified by forming an integral bodystructure with the heating apparatus 3 and the reactor 9.

The reactor 9 is arranged at a position below the ring shaped plate 8.The reactor 9 comprises a catalyst cartridge 10 containing a catalystlayer 11 formed by filling an alumina group catalyst on a metallic mesh16. The alumina group catalyst is a catalyst containing Al₂O₃ of 80% andNiO₂ of 20%. The catalyst cartridge 10 is inserted into the internaltube 7. A cylinder 17 is fixed to the casing 6 by joining the flange 18with the flange 13. The flange 63 of the catalyst cartridge 10 isconfined and held by the flange 13. The reactor 9 comprises a heater forkeeping the reactor at a desired temperature (not shown in the figure)and is arranged between the casing 6 and the internal tube 7. A baffleholder 21 holding a baffle 20 is fixed to the cylinder 17. The coolingapparatus 22 is arranged beneath the baffle holder 21 and is fixed tothe baffle holder 21. Sprays 24 and 25 are provided inside the casing ofthe cooling apparatus 22.

Reaction water, or steam, supplied from the water supplying pipe 32, andair supplied from the air supplying pipe 41 are mixed with the exhaustgas in the piping 31. The water is supplied into the exhaust gas,because the chemical reaction expressed by the equation (2) explainedlater is a hydrolysis reaction. The amount of water, or steam, suppliedis approximately 25 times per one mole of CF₄. The exhaust gascontaining water, air, and CF₄ is heated indirectly by the electricheater 4 while flowing through a path 15 in the heating apparatus 3.Then, the water is converted to steam. The exhaust gas is heated by theelectric heater 4 to approximately 700° C., i.e. a temperature for thedecomposition of CF₄ and is preferably proceeds in the catalyst layer.The temperature control apparatus 30 controls the current flowing in theelectric heater 4 so that the temperature Te of the exhaust gasdetermined by the thermometer 61 at the inlet portion 94 of the reactor9 becomes a preset temperature. This temperature control is used in eachof the following embodiments. The temperature of the catalyst layer 11can be maintained at the reaction temperature by the above temperaturecontrol. In the case of CF₄, the temperature is maintained in the rangeof approximately 650-750° C.

The heated exhaust gas containing CF₄ is supplied to the reactor 9filled with the catalyst. The CF₄ in the exhaust gas reacts with H₂O andis decomposed to HF and CO₂ by the effect of the alumina group catalystin the catalyst layer 11 as expressed by the following equation (2):CF₄+2H₂O=>CO₂+4HF  (2)

In the case when C₂F₆, one type of PFC, is contained in the exhaust gas,C₂F₆is decomposed to CO₂ and HF by the reaction expressed by thefollowing equation (3):C₂F₆+3H₂O+(½)O₂=>2CO₂+6HF  (3)FIG. 6 is a graph indicating decomposition characteristics of PFC by thealumina group catalyst, and the abscissa indicates decompositiontemperature and the ordinate indicates decomposition rate. The aluminagroup catalyst used in the measurement had the composition explainedpreviously. Four kinds of PFC were tested, including CHF₃, CF₄, C₂F₆,and C₄F₈. As the testing conditions, the concentration of a respectivePFC was 0.5%, and SV was 1000/h. The reaction water was added in anamount approximately 10 times that of the theoretical amount. As FIG. 6reveals, all four PFC indicated a decomposition rate near 100% at areaction temperature of approximately 700° C. The decomposition rate ofCF₄ and CHF₃ at approximately 650° C. was equal to or more than 95%, andthe decomposition rate of C₂F₆ and C₄F₈ at approximately 670° C. wasequal to or more than 80%. By using the above catalysts, practicaldecomposition of a PFC in the range of approximately 650-750° C. ispossible.

The high temperature exhaust gas, containing decomposed gases such asCO₂ and HF exhausted from the catalyst layer 11, is conducted to thecooling region 23 in the cooling apparatus 22 through the baffle 20.

The cooling water supplied throughout the water supplying piping 39 and40 are sprayed continuously in to the cooling region 23 by the sprays 24and 25. The exhaust gas at a high temperature is cooled to 100° C. orlower by the sprayed water. A part of the HF is removed from the exhaustgas by dissolving it into the cooling water. The cooling of the exhaustgas at a high temperature can be achieved not only by spraying, but alsoby bubbling the gas into a water tank. The sprayed water is conducted toa lower portion of the acidic gas removing apparatus 98 through thepiping 34 and 35. By providing the baffle 20, the path for conductingthe exhaust gas from the baffle holder 21 to the cooling apparatus 22becomes zigzag, and a back flow of the splashed cooling water sprayedfrom the sprays 24 and 25 into the catalyst layer 11 can be prevented.Therefore, a temperature drop of the catalyst layer 11 caused by thesplashed water can be prevented, and a release of undecomposed PHC canbe avoided.

The exhaust gas containing the decomposed gases (CO₂ and HF) at a lowtemperature, which is exhausted from the cooling apparatus 22, isconducted to the acidic gas removing apparatus 98 through the piping 33.The acidic gas removing apparatus 98 comprises a packed layer 95 filledwith Raschig rings made of plastics and a spray 27 inside for removingHF contained in the decomposed gas at a high concentration, such asapproximately 4% by volume. The spray 27 is arranged above the packedlayer 95. The cooling water supplied through the water supply piping 70is sprayed through the spray 27 and flows down through the packed layer95. The exhaust gas comes into sufficient contact with the cooling waterin the packed layer 95 that a majority of the HF contained in theexhaust gas can be dissolved into the cooling water. The HF in theexhaust gas can be removed significantly by the acidic gas removingapparatus 98 in concentrations from 4% by volume to a several ppm.

The exhaust gas, the acidic gas content of which is decreasedremarkably, is conducted to the duct 45 through the piping 36 byoperating a blower 59 and is released to the outside of the system. Theinsides of the cooling apparatus 22 and the acidic gas removingapparatus 98 are kept at a negative pressure by the operation of theblower 59. Thus, the possibility that hazardous HF contained in theexhaust gas will leak to the outside of the system can be prevented. Thebubbling, method also can be applied to the acidic gas removingapparatus 98. However, with the spraying method, the pressure loss issmaller than that of the bubbling method, and the capacity of the blower59 can be made smaller.

The waste water generated at the silicon removing apparatus 2, thecooling apparatus 22, and the acidic gas removing apparatus 98 iscollected at a lower portion of the acidic gas removing apparatus 98.The waste water contains impurities, such as SiO₂, HF, and others. Thewaste water is conducted to a neutralizer (not shown in the drawing)though the piping 37, by operating the waste water pump 60, and isprocessed. In accordance with the present embodiment, the solidparticles such as SiO₂ are not carried into the catalyst layer 11 in thereactor 3, because the silicon components contained in the exhaust gashave been previously removed by the silicon remover 2 as SiO₂. If thesilicon remover 2 is not provided, SiO₂ is generated by the reactionexpressed by the equation (1) with the water supplied from the watersupplying piping 32 at a portion downstream from the joining point ofthe piping 31 and the water supplying piping 32. When the SiO₂ flowsinto the catalyst layer 11, the following problems (1) and (2) arecaused:

(1) Pores formed on the catalysts are closed by the SiO₂.

(2) Intervals formed among the catalysts are choked.

On account of the above problems (1) and (2), the surface of thecatalyst is decreased, and the decomposition reaction of the PFC isdecreased.

Furthermore, because of the above problem (2), the flow of the exhaustgas in the catalyst is decreased, and the contact of the catalyst withthe exhaust gas is hindered. This causes a decrease in the decompositionreaction of the PFC. In accordance with the present embodiment, SiO₂ ispreviously removed from the exhaust gas by generating the reactionexpressed by the equation (1) at the silicon remover 2, and,accordingly, the above problems are not generated and the efficiency ofdecomposition of the PFC can be improved.

In accordance with the present embodiment, the decomposition processingof the PFC can be achieved with a high efficiency by using the catalyst,and the release of PFC, which is one of gases causing warming-up of theearth, into the atmosphere can be avoided. Furthermore, unreacted COgenerated by the decomposition of CF₄ with the catalyst can be convertedto harmless CO₂ by mixing air into the exhaust gas.

In accordance with the present embodiment, CF₄ can be decomposed at asufficiently lower temperature than the conventional combustion method.Accordingly, necessary utilities, such as heat energy, water, and thelike can be decreased. Application of the present embodiment to asemiconductor manufacturing plant is advantageous even as a safetyaspect against a fire hazard, because the temperature of the decomposedgas is low. The catalyst has a long life, and a recycle use of thecatalyst is possible. Therefore, the operation cost of the plant can bedecreased significantly in comparison with the reagent method.

When an end of life of the catalyst is reached, the catalyst cartridge10 is replaced with a new catalyst cartridge. The exchanging operationwill be explained hereinafter with reference to FIG. 7. The catalystcartridge 10 is held by a flange 13 by fitting a protrusion 64 of aflange 63 into a groove 65 formed inside the flange 13. For detachingand attaching the catalyst cartridge 10, a cartridge detaching andattaching apparatus 66 is used. The cartridge detaching and attachingapparatus 66 comprises a lifter 68, a rotatable base 67 fixed rotatablyto the lifter 68, and a rotary handle 69.

After detaching the cylinder 17, the baffle holder 21, and the coolingapparatus 22 from the casing 6, the cartridge detaching and attachingapparatus 66 is placed under the catalyst cartridge 10. The rotatablebase 67 is elevated by the lifter 68. A rubber plate adhered on thesurface of the rotatable base is brought into contact with the flange63. The rotatable base is rotated by operation of the rotary handle 69.The rotating force is transmitted to the catalyst cartridge 10 via therubber plate. When the protrusion 64 is moved to a designated position,rotation of the rotable base 67 is stopped, and the lifter is retracted.The protrusion 64 is detached from the groove 65, and the catalystcartridge 10 is disassembled from the flange 13 and withdrawn from theinternal tube 7.

Then, a new catalyst cartridge 10 is placed on the rotatable base 67.The new catalyst cartridge 10 is inserted into the internal tube 7 by aprocedure opposite to that of the detaching operation and is attached tothe flange 13. The protrusion 64 of the new catalyst cartridge 10 isadjusted to the above designated position by rotating the rotatable base67. After elevating the lifter 68 somewhat, the protrusion 64 is fittedinto the groove 65 by rotating the rotatable base 67 by operating therotary handle 69. The cylinder 17, the baffle holder 21, and the coolingapparatus 22 are attached to the casing 6. Then, the PFC decompositionprocessing by the PFC decomposition processing unit 76 becomes availableagain.

The exchange of the catalyst cartridge 10 can be performed readily byusing the cartridge detaching and attaching apparatus 66. Becauseoperators do not touch a hot spent catalyst cartridge 10, the operatorsare protected from burning. Because the hot spent catalyst cartridge 10can be detached readily, the time necessary for the exchanging thecatalyst cartridge 10 can be decreased significantly. Because spreadingof catalyst particles and a generation of dust by the exchangingoperation can be prevented, a carrying out of the exchanging operationin the clean room becomes possible.

The present embodiment can be applied to cases of decomposition of thevarious substances indicated in Table 1, such as CF₄, CHF₃, C₂F₆, andC₄F₈. These substances can be decomposed at a reaction temperature ofapproximately 700° C. using an alumina group catalyst. The presentembodiment can be applied to the decomposition of C₂F₆ contained in theexhaust gas from a CVD apparatus, and PFC contained in the exhaust gasfrom an etching apparatus for a liquid crystal display, in addition tothe PFC contained in the exhaust gas obtained from a dry etchingapparatus in a semiconductor manufacturing plant.

An exhaust gas control system for a dry etching apparatus for use insemiconductor manufacturing, wherein a PFC processing apparatus ofanother embodiment of the present invention is applied, will beexplained hereinafter. The exhaust gas control system of the presentembodiment is composed in the same manner as the system indicated inFIG. 1 and FIG. 2 except that each of the PFC processing apparatus, suchas apparatus 1, 1A, and the like, are replaced with a PFC processingapparatus 1C indicated in FIG. 8. The PFC processing apparatus 1C hasthe same composition as the PFC processing apparatus 1, except that thesilicon remover 2 in the PFC processing apparatus 1 is replaced with asilicon removing apparatus 71, and a return piping 75 is newly added.The silicon removing apparatus 71 comprises silicon removers 2 and 72.The silicon remover 72 comprises a spray 73, and a diffusion portion 74filled with packing materials inside a vessel. The silicon remover 72has the same composition as the silicon remover 2 indicated in FIG. 4.The outlet of the piping 29 is oriented downwards in the silicon remover72. The ball check valve 27 is not provided at the outlet side of thesilicon remover 72. The return piping 75 is connected to the piping 37downstream of the waste water pump 60. The vessel of the silicon remover72 is composed of corrosion resistant vinyl chloride, in order toprevent corrosion by HF.

The exhaust gas containing CF₄, SiF₄, and the like is conducted into thevessel of the silicon remover 72 through the piping 29. The exhaust gasascends in the vessel and flows inside the vessel by diffusion throughthe diffusion portion 74. A part of the waste water pumped out by thewaste water pump 60 and supplied via return piping 75 is sprayed throughthe spray 73. The concentration of respective F ions and Si ions in thewaste water pumped out from the waste water pump 60 are less than tensof ppm. The waste water has a sufficient performance for removing the Siand HF. By causing a part of the SiF₄ contained in the exhaust gas tocontact the sprayed waste water, the reaction expressed by the equation(1) occurs. The generated SiO₂ is removed from the exhaust gas by thewaste water, and the HF is dissolved into the waste water.

The exhaust gas exhausted from the silicon remover 72 is conducted tothe silicon remover 2. Fresh water supplied through the water supplypiping 38 is sprayed through the spray 26 of the silicon remover 2. Bycausing the residual SiF₄ contained in the exhaust gas to contact thesprayed water, the reaction expressed by the equation (1) occurs in thesilicon remover 2. The waste water containing the SiO₂ and HF isconducted to the silicon remover 72 and is mixed with the sprayed wastewater from the spray 73. The mixed waste water is conducted to thebottom portion of the acidic gas removing apparatus 98 through thepiping 35. The processes at other portions of the PFC processingapparatus 1C are the same as the processing in the PFC processingapparatus 1.

The PFC processing apparatus 1C generates the same advantages as theadvantages obtained by the PFC processing apparatus 1. Furthermore, thePFC processing apparatus 1C has additional advantages as follows. Thatis, because the amount of the fresh water supplied through the watersupply piping 38 in the PFC processing apparatus 1C is decreased, theamount of waste water conducted to the neutralizer (not shown in thefigure) is decreased. Furthermore, since the reaction expressed by theequation (1) is generated at two portions in the silicon removers 2 and72, the removing efficiency of the Si components, such as SiF₄ and thelike contained in the exhaust gas, is improved.

Another embodiment of the PFC decomposition processing unit is indicatedin FIG. 9. The PFC decomposition processing unit 76A of the presentembodiment comprises a heating apparatus 3A and a reactor 9A. Thecylinder 17, the baffle holder 21, and the cooling apparatus 22 of thePFC decomposition processing unit 76 are also used in the PFCdecomposition processing unit 76A and are arranged on the flange 13 inthe casing 6 in the above order. The reactor 9A comprises a bottomportion 83 in an internal tube 79. A bottom plate 82 is provided at thebottom portion 83 as a slidable member. The catalyst layer 11 filledwith the alumina group catalyst is formed on the bottom plate 82 and thebottom portion 83 in the internal tube 79. The alumina group catalyst isa catalyst containing Al₂O₃ 80% and NiO₂ 20%. A flange 81 of theinternal tube 79 is fixed to the flange 13.

The heating apparatus 3A comprises an internal tube 77, the electricheater 4, and the insulating material 5 covering the electric heater 4.The electric heater 4 and the insulating material 5 are arranged betweenthe internal tube 77 and the casing 6. A flange 78 of the internal tube77 is fixed to the flange 80. A gap 16 is formed between the casing 6and the flanges 78 and 81.

The catalyst which reaches the end of its life can be taken out frominside the internal tube 79 by detaching the cylinder 17, the baffleholder 21, and the cooling apparatus 22, and removing the bottom plate82. The functions of the heating apparatus 3A and the reactor 9A are thesame as the functions of the heating apparatus 3 and the reactor 9 ofthe PFC decomposition processing unit 76. The same advantages asprovided by the PFC decomposition processing unit 6 can be obtained bythe PFC decomposition processing unit 76A.

An exhaust gas control system for the dry etching apparatus in asemiconductor manufacturing plant, to which the other embodiment of thePFC processing apparatus of the present invention is applied, will beexplained hereinafter with reference to FIG. 10, FIG. 11, and FIG. 12.In accordance with the exhaust gas control system of the presentembodiment, plural PFC processing apparatus 1D are arranged in a cleanroom 54. This differs from the embodiments indicated in FIG. 1 and FIG.2. Each of the PFC processing apparatus 1D is connected to separatedpiping 29, respectively.

Details of the PFC processing apparatus 1D are indicated in FIG. 11. ThePFC processing apparatus 1D is of the horizontal type, and comprises thesilicon remover 2 and the PFC decomposition processing unit 76B. Thesilicon remover 2 is connected to the piping 29. The PFC decompositionprocessing unit 76B comprises the heating apparatus 3, a reactor 9B, andthe cooling apparatus 22. The PFC decomposition processing unit 76B doesnot comprise the acidic gas removing apparatus 98. In accordance withthe present embodiment, the acidic gas removing apparatus 98 is providedin the duct 45. The heating apparatus 3 of the PFC decompositionprocessing unit 76B is composed only by arranging the heating apparatus3 of the PFC decomposition processing unit 76 in a horizontal direction.The reactor 9B comprises plural holding plates 84 and 85, which areperforated with a large number of small holes, in the internal tube 7.The catalyst layer 11 is composed by packing and holding the aluminagroup catalyst (containing Al₂O₃ 80% and NiO 20%) between the holdingplate 84 and the holding plate 85. A baffle pate 86 is arranged abovethe catalyst layer 11, as indicated in FIG. 12, and is attached to theinside of the internal tube 7. The baffle 20 is provided inside thecooling apparatus 22. The functions of the heating apparatus 3, thereactor 9B, and the cooling apparatus 22 of the present embodiment arethe same as the functions of the heating apparatus 3, the reactor 9, andthe cooling apparatus 22 of the PFC decomposition processing unit 76.

The PFC processing apparatus 1D provides the same advantages as the PFCprocessing apparatus 1, except for the lack of a contribution of anacidic gas removing apparatus 98. Furthermore, the PFC processingapparatus 1D can be made compact, because it is arranged in a horizontaldirection without providing the acidic gas removing apparatus 98.Accordingly, the PFC processing apparatus 1D can be installed in anexisting semiconductor manufacturing plant, which may scarcely have anextra margin in space for installing such apparatus. That is, the PFCprocessing apparatus 1D can be installed in a piping area above theclean room 54. The PFC processing apparatus 1D requires only a smallspace for installation.

The level of the catalyst in the catalyst layer 11 tends to dropsomewhat with the passage of time; therefore, a slight interval isformed between the upper surface of the catalyst layer 11 and the innersurface of the internal tube 7. Because the baffle plate 86 is arrangedin the catalyst layer 11, by-passing undecomposed PFC gas through thisslight interval to the cooling apparatus 22 can be prevented. The PFCgas is certainly passed through the catalyst layer 11 and decomposed.

Another embodiment of the exhaust gas control system of dry etchingapparatus for use in a semiconductor manufacturing plant will beexplained hereinafter. The exhaust gas control system of the presentembodiment is composed by replacing each of the PFC processing apparatusin the exhaust gas control system indicated in FIG. 1 and FIG. 2 withthe PFC processing apparatus 1E indicated in FIG. 13. The PFC processingapparatus 1E comprises the silicon remover 2, a PFC decompositionprocessing unit 76C, and an acidic gas removing apparatus 98, which isnot shown in the FIG. 13. The PFC processing apparatus 1E is formed byreplacing the PFC decomposition processing unit 78 in the PFC processingapparatus 1 with the PFC decomposition processing unit 76C.

Details of the PFC decomposition processing unit 76C will be explainedhereinafter. The PFC decomposition processing unit 76C differs from thePFC decomposition processing unit 76 in the composition of the casingand the internal tube. The PFC decomposition processing unit 76Ccomprises a casing 88, a heating apparatus 3B for heating an internaltube 77, and a reactor 9B comprising a casing 89 and an internal tube90. The heating apparatus 3B comprises the electric heater 4 and theinsulating material 5 arranged between the casing 88 and the internaltube 77. In the reactor 9B, the catalyst cartridge 10 containing thecatalyst layer 11 is inserted into the internal tube 90. The catalystcartridge 10 is fitted to the flange at the lower end of the casing 89in the same manner as in the PFC decomposition processing unit 76. Thecatalyst layer 11 is filled with the alumina group catalyst describedpreviously. The baffle holder 91 comprising the baffle 20 connects thereactor 9B and the cooling apparatus 22. The flanges of the casing 88,the internal tube 77, and the casing 89 are connected by bolts.

The PFC processing apparatus 1E produces the same advantages as the PFCprocessing apparatus 1. By detaching the above flanges, the heatingapparatus 3B can be separated readily from the reactor 9B. Disassemblingthe catalyst cartridge 10 can be performed in the same manner as in thePFC decomposition processing unit 76.

Another embodiment of the exhaust gas control system of the dry etchingapparatus in the semiconductor manufacturing plant will be explainedhereinafter. The exhaust gas control system of the present embodiment isformed by replacing each of the PFC processing apparatus in the exhaustgas control system indicated in FIG. 1 and FIG. 2 with the PFCprocessing apparatus 1F indicated in FIG. 14. The PFC processingapparatus 1F is obtained by replacing the PFC decomposition processingunit 76 in the PFC processing apparatus 1C with the PFC decompositionprocessing unit 76D. In the PFC decomposition processing unit 76D, aheat exchanger 93 is arranged between the reactor 9 and the cylinder 17of the PFC decomposition processing unit 76. A heat conducting tube 92is arranged in the heat exchanger 93. The piping 32 is connected to theentrance side of the heat conducting tube 92. The piping 32A connectedto the outlet side of the heat conducting tube 92 is connected to thepiping 31 at a point upstream from the merging point of the piping 31and the air supplying pipe 41.

In accordance with the present embodiment, the reaction water suppliedfrom the piping 32 is heated by the exhaust gas at approximately 700° C.exhausted from the catalyst layer 11 to be steam while flowing throughthe heat conducting tube 92. The steam is introduced into the piping 31through the piping 32A. The exhaust gas containing steam, air, and CF₄,which is one type of PFC, is conducted to the catalyst layer 11 via theheating apparatus 3. Then, the reaction expressed by the equation (2) isgenerated in the catalyst layer 11.

The PFC processing apparatus 1F produces the same advantages as the PFCprocessing apparatus 1C. Furthermore, in accordance with the presentembodiment, the heat of the exhaust gas at approximately 700° C.exhausted from the catalyst layer 11 can be recovered by the heatexchanger 93. Accordingly, the heating capacity of the heating apparatus3, and the amount of the cooling water to be supplied to the sprays 25and 26 in the cooling apparatus 23 can be decreased. In accordance withthe present embodiment, the amount of waste water to be conducted to theneutralizer can be decreased to an amount smaller than that of the PFCprocessing apparatus 1C.

1. A method of processing a perfluoride compound, comprising the stepsof: removing SiF₄ from an exhaust gas containing a perfluoride compoundand the SiF₄ by contacting the exhaust gas with water, heating theexhaust gas containing the perfluoride compound, and at least one ofwater and steam added after removal of the SiF₄, after removing theSiF₄, supplying said heated exhaust gas and at least one of water andsteam to a catalyst layer filled with a catalyst which is able todecompose the perfluoride compound contained in the exhaust gas uponcontact with the catalyst, cooling to 100° C. or lower, by water, theexhaust gas containing decomposed gas generated by the decomposition ofthe perfluoride compound, which is exhausted from said catalyst layer,in a cooling apparatus arranged at a portion below said catalyst layer,and releasing the cooled exhaust gas, wherein the cooling step isperformed under a condition that the exhaust gas is kept at a negativepressure.
 2. A method of processing a perfluoride compound as claimed inclaim 1, wherein said exhaust gas to be supplied to said catalyst layeris heated to a designated temperature.
 3. A method of processing aperfluoride compound as claimed in claim 2, wherein said designatedtemperature is in the range of 650° C.-750° C.
 4. A method of processinga perfluoride compound as claimed in claim 1, wherein an acidic gas isremoved from said cooled exhaust gas.
 5. A method of processing aperfluoride compound as claimed in claim 1, wherein said exhaust gascontaining the decomposed gas is cooled by heat exchanging said exhaustgas with cooling water.
 6. A method of processing a perfluoride compoundas claimed in claim 5, wherein said removal of the SiF₄ is performed byusing a first SiF₄ removing apparatus and a second SiF₄ removingapparatus, said exhaust gas exhausted from said first SiF₄ removingapparatus is supplied to said second SiF₄ removing apparatus, saidexhaust gas is brought into contact with water in the second SiF₄removing apparatus, and said exhaust gas containing the SiF₄ is broughtinto contact with both waste water from said second SiF₄ removingapparatus and said cooling water which has contacted said exhaust gascontaining said decomposed gas in said first SiF₄ removing apparatus. 7.A method of processing a perfluoride compound as claimed in claim 1,wherein said steam is generated by heat exchange of water with saidexhaust gas exhausted from said catalyst layer.
 8. A method ofprocessing a perfluoride compound as claimed in claim 1, wherein saidcatalyst is an alumina group catalyst.
 9. A method of processing aperfluoride compound as claimed in claim 1, wherein said exhaust gas isan exhaust gas exhausted from a semiconductor manufacturing apparatus.10. A method of processing a perfluoride compound, comprising the stepsof: removing SiF₄ from an exhaust gas containing a perfluoride componentand the SiF₄ by contacting the exhaust gas with water, adding at leastone of water and steam to said exhaust gas containing the perfluoridecompound, after removing the SiF₄, supplying said exhaust gas containingsaid at least one of water and steam and the perfluoride compound in aregion at an upstream side, in a direction of flow of the exhaust gas,from a catalyst layer in a casing, after removing the SiF₄, the casingbeing provided with a heater inside the casing and being provided withthe catalyst layer, said catalyst layer being filled with a catalyst andis arranged detachably in said casing at a downstream side, in thedirection of flow of the exhaust gas, from said heater, in order to heatsaid exhaust gas with said heater, supplying heated exhaust gas and atleast one of water and steam to said catalyst layer filled with thecatalyst, which is able to decompose the perfluoride compound containedin said exhaust gas upon contact with said catalyst, cooling to 100° C.or lower, by water, the exhaust gas containing decomposed gas generatedby the decomposition of the perfluoride compound in a cooling apparatusarranged at a portion below said catalyst layer, to provide cooledexhaust gas, and releasing the cooled exhaust gas from said coolingapparatus, wherein said cooling step is performed under a condition thatthe exhaust gas is kept at a negative pressure.
 11. A method ofprocessing a perfluoride compound as claimed in claim 10, wherein theexhaust gas containing at least one of water and steam and theperfluoride compound is supplied into an upper region of the casing,which is provided with the heater, for heating by the heater, and theheated exhaust gas is supplied into the catalyst layer, which isarranged at a lower part of the casing in a manner that the catalystlayer is removable in a lower direction from the casing.
 12. A method ofprocessing a perfluoride compound as claimed in claim 3, wherein saidperfluoride compound includes CF₄.
 13. A method of processing aperfluoride compound as claimed in claim 1, wherein said perfluoridecompound is at least one selected from the group consisting of CF₄, CF₆,NF₃, CHF₃, C₄F₈, C₃F₈ and SF₆.
 14. A method of processing a perfluoridecompound, comprising the steps of: removing SiF₄ from an exhaust gascontaining a perfluoride compound and the SiF₄ by contacting the exhaustgas with water, heating the exhaust gas containing the perfluoridecompound and at least one of water and steam added, after removal of theSiF₄, after removing the SiF₄, supplying the heated exhaust gas and atleast one of water and steam to a catalyst layer filled with a catalystwhich is able to decompose the perfluoride compound contained in theexhaust gas upon contact with the catalyst, cooling to 100° C. or lower,by water, the exhaust gas containing decomposed gas generated by thedecomposition of the perfluoride compound, which is exhausted from saidcatalyst layer, in a cooling apparatus arranged at a portion below saidcatalyst layer, and releasing the cooled exhaust gas from said coolingapparatus, wherein cooling water, which has been supplied to saidcooling apparatus and used for cooling said exhaust gas, and waterpreviously used for removing SiF₄ in the step of removing SiF₄, are usedfor removing SiF₄ in the step of removing SiF₄ by contacting withexhaust gas containing SiF₄, and wherein the cooling step is performedunder a condition that the exhaust gas is kept at a negative pressure.15. A method of processing a perfluoride compound, comprising the stepsof: removing SiF₄ from an exhaust gas containing a perfluoride compoundand the SiF₄ by contacting the exhaust gas with water, adding at leastone of water and steam to said exhaust gas containing the perfluoridecompound, after removing the SiF₄, supplying said exhaust gas containingsaid at least one of water and steam and the perfluoride compound in aregion at an upstream side, in a direction of flow of the exhaust gas,from a catalyst layer in a casing, after removing the SiF₄, the casingbeing provided with a heater inside the casing and the catalyst layer,said catalyst layer being filled with a catalyst and is arrangeddetachably in said casing at a downstream side, in the direction of flowof the exhaust gas, from said heater, in order to heat said exhaust gaswith said heater, supplying heated exhaust gas and at least one of waterand steam to said catalyst layer filled with the catalyst, which is ableto decompose the perfluoride compound contained in said exhaust gas uponcontact with said catalyst, cooling to 100° C. or lower, by water, theexhaust gas containing decomposed gas generated by the decomposition ofthe perfluoride compound in a cooling apparatus arranged at a portionbelow said catalyst layer in order to provide cooled exhaust gas, andreleasing the cooled exhaust gas from said cooling apparatus, whereincooling water, which has been supplied to said cooling apparatus andused for cooling said exhaust gas, and water previously used forremoving SiF₄ in the step of removing SiF₄, are used for removing saidSiF₄ in the step of removing SiF₄ by contacting with said exhaust gascontaining said SiF₄, and wherein said cooling step is performed under acondition that the exhaust gas is kept at a negative pressure.
 16. Amethod of processing a perfluoride compound as claimed in claim 1,wherein said cooling by water includes supplying a water spray to theexhaust gas in the cooling apparatus.
 17. A method of processing aperfluoride compound as claimed in claim 10, wherein said cooling bywater includes supplying a water spray to the exhaust gas in the coolingapparatus.
 18. A method of processing a perfluoride compound as claimedin claim 14, wherein said cooling by water includes supplying a waterspray to the exhaust gas in the cooling apparatus.
 19. A method ofprocessing a perfluoride compound as claimed in claim 15, wherein saidcooling by water includes supplying a water spray to the exhaust gas inthe cooling apparatus.